How can I solve problems with Remesh modifier?
I guess it's not bug, as the Remesh Modifier page on Blender 2.79 Manual explain this problem and how to solve it :


Just add a Solidify Modifier, set the Thickness to 0.5, and make sure the Solidify Modifier is processed before the Remesh Modifier but after the Ocean Modifier. The order of the modifiers should be, from top to bottom : Ocean / Solidify / Remesh.